Warm April Weather

April 3, 2007

SnapshotSnapshot2Obviously today was not the warm April weather I refer to in the title.  Clouds were a bit thicker and showers a bit more widespread than I was expecting this afternoon. 
00z models are in and they look quite similar to earlier model forecasts for the next few days.  We have one more day of cloud cover and light showers tomorrow.  Then a developing strong ridge of high pressure pushes clouds and rainfall to the north for Thursday and Friday.  850mb temps on GFS, WRF, and MM5 reach the +11 or +12 mark Friday.  At the same time easterly offshore flow returns from Thursday morning through Friday midday, then the wind turns calm Friday afternoon.  This setup has given us "surprisingly" high temperatures many times in my forecasting career here in Portland (which would be my entire career).  The Mark Nelsen "magic chart" I use for warm season forecasting gives us a high of 75 with no easterly wind, as high as 81 with perfect easterly flow conditions.  If maps are correct and nothing changes, we could hit 80 at PDX on Friday.
Beyond that, another interesting change in the GFS this evening (but not in WRF).  It shows the Saturday system approaching the coast becoming more cutoff and sending southeasterly flow up over us during the day.  That’s a thunderstorm pattern in the Northwest from April to September.  In the long range, cooler and wetter weather is back beginning possibly as early as Easter Sunday, but more likely Monday…Mark